Massive Intravenous Infusions *

Some of the factors governing the development of edema in the lungs are understood in broad terms. These factors are considered to be no different from those operative in the systemic vessels-increased hydrostatic pressure, decreased oncotic pressure, excessive permeability of the vessels, and decreased lymphatic drainage. Little specific quantitative information is available relative to the pulmonary vasculature. Thus, although drainage from the lung by way of the lymphatics has been shown to increase during the development of pulmonary congestion and edema,' a study of the role of the lymphatics in the pathogenesis of edema has not been adequately approached. Anoxia is said to increase the permeability of the capillaries in the periphery, but its effect on those of the lungs is not known. It must also be remembered that other than capillary vessels participate in the exudative process; the role of the venules has recently been emphasized." In the lung the protein osmotic pressure normally exceeds capillary hydrostatic pressure by a considerable margin, the opposite of the condition in the arterial ends of systemic capillaries. Thus it is possible to introduce large quantities of water via the trachea with very rapid absorption. Still adumbrated as are these various factors, it has become plain that they are interrelated and that pulmonary edema in no instance depends upon a single pathogenetic mechanism. For example, the very formation of the edema fluid involves some leakage of protein into the extravascular compartment. Also, as the alveoli become filled with exudate, an increasing barrier is interposed between the walls of the vessels and the oxygen of the atmosphere. The complexities of these interrelationships became apparent in a study of the effects of increased intracranial pressure on the lesser circulation.' During these experiments, considerable quantities of saline fluid were introduced into the blood stream over a period of several hours, directly or via the subdural or subarachnoid space. The present observations are thus partly in the nature of a control study. Previous studies of the effects of infusions of fluid have been variously interpreted. In part, contradictory statements have resulted from lack of